Two kinds of 3D label free Bio-Transfer-Standards (BTS) have been further developed at the University of Helsinki (UH). The first one, NanoRuler, is a staircase BTS featuring eight fatty acid bilayers which allows vertical calibration in the range of 5 to 40 nm. The second one, NanoStar, is a V-shaped BTS featuring two 5 nm tall bilayers that overlap at 10° angle. This standard enables the determination of the Instrument Transfer Function (ITF). A stability test was conducted on the BTSs, during which the standards were stored in laboratory conditions, and were profiled each week. Profiling was done using a custom-built Scanning White Light Interferometer (SWLI). The stability of NanoStar was ± 0.3 nm, and of NanoRuler ± 0.5 nm to ± 2.5 nm. The BTSs maintained their specified properties for at least six months and therefore allow vertical calibration and ITF determination. In addition, changes in surface morphology of one NanoRuler subjected to water immersion are presented. This paper reports intermediate findings during an ongoing stability test that will run for 24 months.
A stair case height Bio-Transfer-Standard (BTS), developed and produced at the University of Helsinki (UH), was measured in two laboratories. The Round Robin test aims to determine whether BTS works with different optical profilers in different laboratories. First the artefact was measured at UH using a custom-built Scanning White Light Interferometer. Then BTS was measured at Sensofar-Tech, S.L. using an S-neox-type interferometer working either in Phase Shifting Interferometry mode or in Imaging Confocal Microscopy mode. To remove the influence of system calibration, a method featuring sample shifting and measurement subtraction was used. The BTS features eight lipid bilayer steps that each are 4.6 ± 0.1 nm tall on average. All 30 measurements done by four different operators at the two laboratories agree to within 0.1 nm which agrees with theoretical estimates and with measurements done using a surface plasmon resonance technique. The Round Robin results show the applicability of the newly developed bio-imaging transfer standard for calibrating 3D optical profilers.